Opus 25: Serenade for Flute, Violin and Viola in D major (1801), This seven part work again harks back to 18th c. serenade music, such as in the Entrata march and the two minuets. The emotional heart is the andante, a set of variations, but on the whole this is a rather slight work.
Something entirely different is Opus 26: the Piano Sonata No. 12 in A-flat major (1801). The structure of the sonata is unconventional in that the piece opens with a slow movement in the format of a theme and variations. After a scherzo follows a funeral march (played by a brass band at Beethoven's own funeral). The sonata closes with a joyful rondo. Beethoven wrote this work out of a sense of competition when the piano virtuoso Cramer visited Vienna. It sets off a new phase of experimentation, now also with form. A memorable sonata.
Experiments with form continue in Opus 27: Two Piano Sonatas (1801) "in the form of a fantasia." The Piano Sonata No. 13 in E-flat major is the more conventional of the two, although all four movements are connected in one continuous flow. It is full of ideas and like its companion starts with simple and intimate music. The Piano Sonata No. 14 in c-sharp minor is the famous "Moonlight" - this time starting with a real slow movement, where the melody seems to rise up out of the chordal mass. This well-known movement is followed by an elfin dance and a volcanic eruption in the finale.
Opus 28: the Piano Sonata No. 15 in D major (1801) reverts to the classical four-movement model. It has an easy-going manner. The emotional core is the andante, which sounds like a solitary walk. The rustic finale with a droning bass has given the sonata the nickname "Pastoral," but that was not a choice of Beethoven himself.
Opus 29: String Quintet in C major (1801). This Beethoven's only original contribution to the string quintet genre, an expansive work with lots of sonority, but in my view falling short of the string quartets op. 18. (String quintets were popular as arrangements of other works as well. Beethoven himself arranged his octet for wind and his third piano trio for this medium; others made string quintet versions of Beethoven's Septet and First Symphony).
Opus 30: Three Violin Sonatas (1803). The Violin Sonata No. 6 in A major is a gracious work, neatly sharing its elegant melodies between the two instruments.The finale is a theme with variations. The Violin Sonata No. 7 in c minor is the largest and most serious of the set, as already indicated by the key. It is in four movements and starts with a mysterious, questioning theme followed by militaristic rumblings. The next adagio possesses great poise and beauty and the fine finale ends uncompromisingly in the minor. The Violin Sonata No. 8 in G major is charming, sturdy and deceptively simple.
Opus 31: Three Piano Sonatas (1802). Although these sonatas share the same opus number, they are very different in character. The Piano Sonata No. 16 in G major is a bright and serene piece. Interesting is the limping melody in the first movement. Sonata No. 17 in d minor with the nickname "Tempest" is indeed volatile and tempestuous, although there is no connection with Shakespeare's play. Piano Sonata No. 18 in E-flat major ("Hunt" was not Beethoven's name) is a relaxed and sunny work, with a scherzo and a minuet as the two middle movements instead of a slow movement. The last movement has a swinging rhythm.
Opus 32: Song – An die Hoffnung (1805). First setting of Tiedge's "Urania," an appeal to hope not unlike Schiller's "Ode to Joy." This was the first vocal work in Beethoven's opus catalogue.
Opus 33: Seven Bagatelles for piano (1802). Beethoven's first larger work for amateurs and the first of three such groups he wrote. The name "bagatelle" originated with Couperin. These are indeed graceful little works.
Opus 34: Six variations on an original theme for piano in F major (1802). These variations are in "a new manner" as Beethoven himself indicated, being all in different keys. Opus 35: Fifteen variations and a fugue for piano on an original theme in E-flat major ("Eroica Variations") (1802). Here, too, we have different keys for all variations. The theme is more memorable than in op. 34 and the work more expansive, too.
Opus 36: Symphony No. 2 in D major (1803). Another symphony in the late-Haydn mold. In comparison with the first symphony, there is a striking brusqueness and almost grotesque humor. The first movement has a great nervous energy. The Larghetto is a relaxing interlude, the Scherzo is full of dynamic contrasts and the finale brings an explosive conclusion to the work.
Opus 37: Piano Concerto No. 3 in C minor (1803). This concerto consolidates the achievements of the first two piano concertos. It is rather "classicizing," especially in the first movement with its orchestral introduction. It became the model for Hummel, Weber and others until Chopin. The most extraordinary movement is the Largo, played almost wholly with the dampers raised, and in character very much like a nocturne.
We skip opus 38: Piano Trio in E-flat major, as this is an arrangement of the Septet, Opus 20.
Opus 39: Two Preludes through all twelve major keys for piano (1789) - two fourteen year old student exercises that Beethoven managed to sell when he was in need for money.
Opus 40: Romance for Violin and Orchestra No. 1 in G major (1802). Simple and sweet music. Begins with double stops for the solo violin and ends with an energetic tutti.
We can also skip Opus 41: Serenade for Piano and Flute or Violin in D major (1803), as this is an arrangement of the flute trio op 25, and Opus 42: Notturno for Viola and Piano in D major (1803), an arrangement of the serenade for string trio op. 8. It is even doubtful whether Beethoven made these arrangements himself.
Opus 43: The Creatures of Prometheus, overture and ballet music (1801). Theater music, consisting of an overture and 17 short pieces of ballet music. Beethoven considered Prometheus' self-sacrifice (the god stole fire from Zeus and gave it to humans) as the highest form of heroic action and would reuse the melody from the last part of the ballet to greater effect in the Eroica Symphony. I found this ballet music rather down to earth.
Opus 44: Piano Trio No. 10 (Variations on an original theme in E-flat major) (1792). Again an old work sold when Beethoven needed money. In the early 90s Beethoven wrote many similar sets of variations.
Opus 45: Three Marches for Piano, 4 hands (1803). Light music as Beethoven wrote in the early 90s when he produced this type of music for wind band.
Opus 46: Song – Adelaide (1795). This second song with an opus number is a weighty work, both as regards the piano part that sometimes overbalances the text and the dramatic singing which reminds more of the opera house than the drawing room. Apparently, the poet, Friedrich Matthison, was not amused.
Opus 47: Violin Sonata No. 9 in A major ("Kreutzer") (1802). A great sonata (also literally, as it last 40 minutes) with a very demanding violin part and broad emotional scope, from the furious first movement to the meditative second and exuberant third. It is almost like a violin concert.
Opus 48: Six Songs (1802). A series of sacred songs on texts by Gellert dating from 1757 and already set by C.P.E. Bach (No. 1: "Bitten," No. 2: "Die Liebe des Nächsten," No. 3: "Vom Tode," No. 4: "Die Ehre Gottes aus der Natur," No. 5: "Gottes Macht und Vorsehung," No. 6: "Bußlied"). Beethoven was inspired by the unity of mankind that speaks from these songs. His renderings are remarkably contained.
Opus 49: Two Piano Sonatas (1792). Piano Sonata No. 19 in G minor. Piano Sonata No. 20 in G major. Again two older works, written about the same time as the first piano sonatas op. 2. It is possible that Beethoven never wanted to publish these sweet and uncomplicated pieces, but apparently his brother offered them to a publisher without Beethoven's knowledge (to make money on the sly?).
Opus 50: Romance for Violin and Orchestra No. 2 in F major (1798). A simple and poetic Adagio Cantabile. More virtuoso and lyrical than the Romance Op. 40.
Conclusion: What struck me in this part of Beethoven's opus, related to the early 1800s, is the amount of recycling of older work (as in the piano sonatas op 49, the variations for piano trio, the two preludes etc.) and the composition of more popular works for a larger group of consumers (the flute trio, the bagatelles, the ballet music for Prometheus, the marches for piano) and the fact that we have also two arrangements of own work. Beethoven now was famous enough to be able to sell some old or inferior work for good money and who can blame him for it?
But there are lots of great works among these opus numbers, too, such as the third piano concerto, the second symphony, the Kreutzer Sonata and the many piano sonatas (except op 49) where Beethoven expands his experiments to include the form of the sonata.